The present invention relates to an attenuation-free electronic switch, particularly for use as a semiconductor crosspoint in switching networks utilized in space-division telephone exchanges, the switch being of the type which includes semiconductors arranged in series to the line to be switched to serve as switching elements which are connected as an open circuit stable negative resistance so that in the ON-state, the elements permit signals to pass in both transmission directions without ON-attenuation.
Attenuation-free electronic switches are disclosed, for example, in German Auslegeschrift (Published Patent Application) No. 2,156,166, and its counterpart, British Pat. No. 1,409,895. Compensation of ON-attenuation is there effected by a controllable semiconductor combination consisting primarily of transistors and acting as a switch which, in its ON-state, has a given negative resistance value and forms a variable open circuit stable negative resistance, as disclosed in FIGS. 6 and 7 and described on page 2 and page 3, column 1 of British Pat. No. 1,409,895.
When this switch is used as a crosspoint in the switching network of a space-division telephone exchange, difficulties arise with respect to ON- an OFF-attenuation because a plurality of crosspoints of this type are connected to one column of a crosspoint array in the switching network. If the control transistor disposed in the shunt-branch switches on the associated crosspoint while the other crosspoints connected to the same column are in the OFF-state by their conductive and saturated control transistors, the crosspoint in the ON-state is attenuated additionally by the crosspoints in the OFF-state connected to the same column line.
The solution proposed in British Pat. No. 1,409,895 can be dependably realized only in a circuit constructed according to the hybrid technique. Construction according to monolithic integration techniques will result in considerable fluctuations in the circuit parameters. In particular, the additional attenuation will be fully evident in the crosspoint array.